Immune System Support: the Basics

There are a lot of products out there which claim to support the immune system - some are beneficial and some are just unsubstantiated hype - and most are expensive. So what should you do if you feel your horse needs some help to stave off winter stress or to make it less likely he'll catch what the horse down the road has?

Immune system support starts with some basics which should be included in every horse's diet.  Before considering any expensive "specialty" products, make sure your horse's diet includes:

• Clean water at a drinkable temperature.  If you use automatic waterers, buckets or tanks should also be available.  Every winter I hear from someone who's horse went without water for a day or longer because the auto waters froze up.
• Salt is often overlooked but is important to encourage adequate hydration.  A 1000 lb horse should receive an ounce of salt (about 4 teaspoons/day) year round.
• Inadequate sodium (from salt) can lead to dehydration at a "cellular" level which can impede or obstruct normal cellular metabolism.
• Plain white table salt is best.  "Designer" salts make attractive door stops but may contain high levels of undesirable minerals.
• If your supplement contains less that the minimum requirement for iodine (most only contain 2 mg) use iodized salt which contains about 1.7 mg iodine per ounce.
• Adequate quality forage, preferably mainly grass hay, with additional provided as needed for colder temperatures.  (See the Cold Weather Feeding Chart.)
• If you feed mainly Bermuda hay and your horse doesn't seem to be looking/feeling his best, consider replacing some of the hay (up to half) with Timothy pellets.  The added cost can pay off in improved condition and good health. 

• Avoid feeds with high levels of simple sugars and starch (which converts to glucose) as excessive glucose can support inflammation.  The processing of "senior" feeds does help greatly with improving digestibility but some contain excessive starch. Look for high fiber feeds as these will be more apt to promote good gut health.  Or give your senior horse a 50/50 combination of beet pulp and steamed or crimped oats plus hay and/or Timothy pellets, along with a quality supplement,  for a nutritious senior diet. 
• Avoid feeds and supplements with "added" iron.  Excess iron can help fuel inflammation and many forages already supply excessive levels of iron.
• Look for a supplement which provides at least the minimum daily requirement for copper, zinc, iodine and selenium. For a 1000 lb horse these are:
• Copper 90-125 mg
• Zinc 360 mg
• Iodine 3.2 mg
• Selenium 1 mg
• Vitamin E and Omega-3 are important antioxidants which decline rapidly when hay is cut and cured.  

• For best immune support, provide vitamin E at a rate of 1000 IU per 500 lbs of body weight (2,000 IU for a 1,000 lb horse). It doesn't matter if the vitamin E is synthetic or natural but it does need fat for absorption.  Using human gel caps which also contain oil is best, otherwise add a small amount of oil at feeding time.  For an inexpensive oil which also adds a small benefit from medium chained triglycerides, try Costco's Mediterranean Blend (canola, olive and grape seed oils).
• The simplest and most cost effective source for Omega-3 is flax. Provide about 2 ounces/day of fresh ground flax seed (which can be pre-ground and stored in the refrigerator) or stabilized flax - HorseTech NutraFlax, Omega HorseShine or Triple Crown OmegaMAX.
• Iodine and selenium are both important for adequate thyroid functioning.
• If your supplement has inadequate iodine, use iodized salt or the original Source meal which has a guaranteed level of iodine. If using another kelp or seaweed product, check that the iodine level is guaranteed.
• Most supplements include selenium at about 2 mg per serving (2 mg per day). If blood tests show low selenium levels, you may need to use a selenium yeast product such as Platinum Selenium Yeast at a higher than usual dosage to bring the level up.  I feel  using an oral selenium yeast algorithm is safer than selenium injectables. 

The above list is what should be included in any horse's diet to ensure a healthy immune system. But older horses or those who are stressed or already ill can benefit from some additional nutrients:

• Vitamin A - around 15,000 IU/day.  Vitamin A losses in hay occur over time; if hay is over six months since cutting it should be supplemented.  Many supplements provide this or you can use human gel caps.
• Vitamin D - horses are able to synthesize their own vitamin D and it is also stored in the liver, usually in quantities sufficient to carry most horses through the winter.  If supplementing, stay close to the minimum requirement (3,000 IU for a 1000 lb horse) as excessive D can be toxic. Again, if not provided in your supplement you can add human gel caps.
• Glutamine - this is an amino acid which is being added more frequently to equine probiotics.  It has been shown to be protective for the mucous membrane lining of the intestines which may help support the intestinal flora production of some immune modulators. 
• There has been more research lately showing the importance of the intestinal lining and intestinal flora in maintaining immunity.
• Cost to provide glutamine is about $0.44 for 10 grams per day. See the links below.
• B-vitamins - not likely deficient except in stressed horses or those with gut issues.  May be included in supplements or can try a human "multi-B" tablet.  
• Adding yeast (Saccharomyces cerevisiae - Diamond V or Yea Sac) can help provide a substrate for intestinal flora, which synthesize the B vitamins, to thrive.

I'd certainly consider these basic and cost effective additions to my horse's diet before moving on to more exotic - and pricey - immune support therapies.

Warm regards,

Patti
in windy Vail AZ

Links:

Flax

HorseTech Nutra Flax http://www.horsetech.com/nutra-flax.html

Omega Fields HorseShine http://www.omegafields.com/equine-products/omega-horseshiner.html

Triple Crown OmegaMax http://www.triplecrownfeed.com/products/supplements/triple-crown-omega-max-omega-3-oils-horse-health/

Glutamine  MyBestHorse http://www.mybesthorse.com/productsorderhere.html 

                   and PureBulk http://purebulk.com/l-glutamine-powder.html#.Uq3-1ZH-nfM

Selenium Yeast

Platinum http://www.platinumperformance.com/equine-selenium-yeast/productinfo/eselp1

HorseTech http://www.horsetech.com/selen.html

Vitamin E and Omega-3 Information and links to sources

http://www.desertequinebalance.com/supplements/vitamin-e
http://www.desertequinebalance.com/supplements/omega-3

Yeast

Purchase Diamond-V Saccharomyces cerevisiae locally at feed mills for best prices

HorseTech Yeast+ http://www.horsetech.com/yeast-plus.html 

Reasonably priced "general" supplements 

HorseTech High Point

http://www.horsetech.com/high-point-alfalfa.html (the "alfalfa" should be used with Bermuda)

http://www.horsetech.com/high-point-grass.html (use with cool season grasses, Timothy pellets)

Source Focus Hoof

http://www.valleyvet.com/ct_detail.html?pgguid=2e87bf0a-7b6a-11d5-a192-00b0d0204ae5&gas=Source

Cold Weather Feeding Chart and Calculator
http://www.desertequinebalance.com/Files/handy-calculators

Iodine - Too Much or Not Enough?

In the latest issue of a well known equine publication, an article on thyroid dysfunction suggests that "...most equine diets of hay and pasture grass (other than in the Pacific Northwest) contain far more than the daily required level of iodine...", and, in a sidebar, cautions that supplementation of iodine could worsen a suspected thyroid issue. Also overlooked here is the small but important role selenium plays in thyroid function.

Iodine deficient soils in the United States

Let's look at some of the facts about iodine.

The National Research Council (NRC), based on the best evidence availablle, suggests a dietary requirement of iodine for horses as a range and recommends using the average of that range as a minimum target.

Suggested range 0.1-0.6 mg Iodine per kilogram of drymatter (DM)
Average of range (0.1-0.6 mg I/kg DM) 0.35 mg I/kg DM

This can also be expressed as a weight-based requirement, presuming the horse has a daily feed intake at 2% of its body weight (BW), which works out similar to the above average.

Maintenance requirement 0.007 mg/kg BW
For a 1000 lb horse,  455 kg x 0.007 = 3.18 mg Iodine/day

For a 1000 lb (455 kg) horse taking in 2% of BW (9.1 kg DM) using the "range" above

low   0.10 * 9.1 = 0.91 mg Iodine (NRC questions if this concentration is sufficient)
avg  0.35 * 9.1 = 3.185 mg Iodine
high  0.60 * 9.1 = 5.46 mg Iodine

(Pregnant or lactaing broodmares have a higher recommended requirement of 0.4 mg I/kg DM.)

The maximum tolerable level for iodine has been set at 5 mg I/kg DM, or 45.5 mg for a 1,000 lb (455 kg) horse.  In a few instances (AZ horses on CAP water, high nitrates in hay, which I now always check in Southwestern hays and other grass hays with high protein levels) I will double the NRC recommendation but otherwise stick with the mid to high range.

From NRC - "Iodine toxicity [seen as goiter] usually results only when iodine is oversupplemented or when animals are receiving feeds containing unusually high amounts of iodine such as some types of seaweed." but toxicity in mares receiving as little as 40 mg a day has been reported.

Iodine concentrations in most common feedstuffs range from 0 to 2 mg/kg DM (equivalent to 0 to 18 mg in 20 lbs or 9.1 kg of hay) depending on the iodine concentration in the soil in which they are grown.  As with other minerals, many conditions can affect forage uptake of iodine from the soil and different farming practices may deplete or concentrate available levels.

Depending on free-choice intake of iodized salt to supply iodine requirements has been shown to result in iodine deficiency in pregnant mares resulting in leg abnormalities in foals, and even when iodized salt is directly added to the feed, the amount may not meed NRC requirements.

Without going overboard, ensuring an Iodine intake level equal to the standard NRC recommendation of 0.35 ppm up to the "high" range of 0.6 ppm might also provide insurance against uptake of the [very] low levels of I-131 detected by Environmental Protection Agency (EPA) monitoring and other environmental "insults".

It is unlikely that using even the higher suggested range would tip your horse over the maximum tolerable level even if your forage contains a fairly high level of iodine. But we should also keep in mind that there is little direct equine research on iodine; without this it's difficult to consider levels higher than those which have been documented to cause goiter in studied horses - 5 mg I/kg DM, or 45.5 mg for a 1,000 lb (455 kg) horse.

Iodine testing for hay and forage is not readily available at most forage labs in the US; when it is the cost may be prohibitive.  For example, at Cumberland Valley Analytical Lab, the price for their Iodine test is $75. On the other hand, if your horse is experiencing issues you feel may be related to excessive iodine intake, the cost may be a worthwhile investment.

Iodine serum level testing (Iodine Total and Iodine Inorganic) is offered at the Michigan State Diagnostic Center. From their Iodine Testing document :

Total serum iodine and particularly serum inorganic iodine reflect the current dietary iodine consumption. Serum inorganic iodine is a good short-term measure of iodine consumption and will reflect excessive iodine supplementation, when present.

Often overlooked when considering possible thyroid dysfunction is selenium deficiency - selenium is necessary for conversion of the inactive hormone T4 to the active thyroid hormone T3 and selenium deficiency together with high iodine intake may result in low T4 levels and other thyroid issues.
http://www.ncbi.nlm.nih.gov/pubmed/9187638  Selenium level testing in whole blood in horses is readily available and also easily included in forage testing (generally under $40).

In summary, iodine is but one element of an overall mineral balanced equine diet. As with any other mineral or supplement, targeting just one nutrient without taking into account how all nutrients interact with one another is not likely to produce the desired results.

Don't throw away the iodized salt or iodine supplement but do make sure that protein, calories, major minerals and other trace minerals are balanced and appropriate for the horse's age, weight, work and reproductive status.  Check that any kelp or seaweed products you use contain guaranteed levels of iodine. "Sea salt", despite the reassuring name, often contains only minute traces of iodine and can't be relied on as an iodine source.

The next time your vet draws blood consider having her check a selenium level - especially if it's been suggested to add a "thyroid" supplement. It makes little sense to use a drug to correct a basic trace mineral deficiency - adding the NRC recommended levels of iodine and selenium may help normalize thyroid function test results.

Warm regards,

Patti in monsoon flooded Vail Az
Don't forget the salt!


Links
Nutrient Requirements of Horses, Sixth Revised Edition  (NRC 2007) Pages 91-92.
http://www.nap.edu/catalog.php?record_id=11653

My previous post about iodine - not much has changed
http://desertequinebalance.blogspot.com/2006/10/iodine-requirement-in-equine-rations.html
and thyroid (including links to Dr. Eleanor Kellon's "Understanding Thyroid" article in Holistic Horse)
http://desertequinebalance.blogspot.com/2013/02/understanding-thyroid.html

Cumberland Valley Analytical Services
http://www.foragelab.com/Lab-Services/Forage-and-Feed/Price-List

Iodine Deficient Soils Map
http://www.goatworld.com/articles/nutrition/iodine.shtml

Michigan State Diagnostic Center for Population and Animal Health
http://www.animalhealth.msu.edu/Bin/Catalog.exe?Action=Test&PAGE=12&Id=2236
http://www.animalhealth.msu.edu/Bin/Catalog.exe?Action=Test&PAGE=12&Id=2920
http://www.animalhealth.msu.edu/Sections/Nutrition/WEBCD.Nutr.REF.003.pdf